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Homocysteine

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Also known as: Plasma Total Homocysteine; Urine Homocysteine; Homocysteine Cardiac Risk
Formal name: Homocysteine

At a Glance

Why Get Tested?

To help determine if you are folate-deficient or vitamin B12-deficient; to determine if you are at increased risk of heart attack or stroke; to help diagnose a rare inherited disorder called homocystinuria

When to Get Tested?

When your healthcare provider suspects that you have a vitamin B12 or folate deficiency; when you have had a heart attack or stroke and do not have traditional risk factors, such as unhealthy lipid levels; as part of routine newborn screening or when a health practitioner suspects that an infant or young person may have homocystinuria

Sample Required?

A blood sample taken by needle from a vein in the arm; sometimes a urine sample in addition to the blood sample

Test Preparation Needed?

You may be instructed to fast for 10 to 12 hours prior to this test.

The Test Sample

What is being tested?

Homocysteine is an amino acid that is typically present in very small amounts in all cells of the body. That is because the body normally converts homocysteine into other products quickly. Since vitamins B6, B12, and folate are necessary to metabolize homocysteine, increased levels of the amino acid may be a sign of deficiency in those vitamins. This test determines the level of homocysteine in the blood and/or urine.

Elevated homocysteine may also be related to a higher risk for coronary heart disease, stroke, peripheral vascular disease (fatty deposits in peripheral arteries), and hardening of the arteries (atherosclerosis). Several mechanisms have been proposed for how homocysteine leads to cardiovascular disease (CVD) risk, including damaging blood vessel walls and supporting the formation of inappropriate blood clots, but direct links haven not been confirmed. There are also several studies that indicate no benefit or lowering of CVD risk with folic acid and B vitamin supplements. So far, the American Heart Association does not consider it a major risk factor for heart disease.

A rare inherited condition called homocystinuria (also called cystathionine beta synthase deficiency) can also greatly increase homocysteine in the blood and urine. In homocystinuria, one of several different genes is altered, leading to a dysfunctional enzyme that does not allow the normal breakdown of the precursor to homocysteine, called methionine. Methionine is one of the eleven essential amino acids that must come from the diet because the body cannot produce it.

Without the proper enzyme to break them down, homocysteine and methionine begin to build up in the body. Babies with this condition will appear normal at birth but within a few years begin to develop signs such as a dislocated lens in the eye, a long slender build, long thin fingers, skeletal abnormalities, osteoporosis, and a greatly increased risk of thromboembolism and of atherosclerosis that can lead to premature CVD.

The buildup in the arteries may also cause intellectual disability, mental illness, slightly low IQ, behavioral disorders, and seizures. Some of those may be alleviated if the condition is detected early, which is why all states screen newborns for homocystinuria.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm. Sometimes a urine sample is also collected.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

Fasting for 10 to 12 hours may be required prior to blood testing.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Clarke R, Bennett DA, Parish S, Verhoef P, Dötsch-Klerk M, et al. (2012) Homocysteine and Coronary Heart Disease: Meta-analysis of MTHFR Case-Control Studies, Avoiding Publication Bias. PLoS Med 9(2): e1001177. doi:10.1371/journal.pmed.1001177. Accessed February 2014.

Pagana, K. D. & Pagana, T. J. (© 2013). Mosby's Diagnostic and Laboratory Test Reference 11th Edition: Mosby, Inc., Saint Louis, MO. Pp 537-538.

(Updated Feburary 2012). Homocystinuria. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001199.htm through http://www.nlm.nih.gov/. Accessed February 2014.

(Updated 2010 July). Coronary Artery Disease | High Homocysteine Level: How It Affects Your Blood Vessels. Familydoctor.org. Available online at http://familydoctor.org/online/famdocen/home/articles/249.html through http://familydoctor.org. Accessed February 2014.

(Reviewed 2011 July). Homocystinuria. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria through http://ghr.nlm.nih.gov. Accessed February 2014.

(Updated 20 January 2012). Homocysteine, Folic Acid and Cardiovascular Disease. American Heart Association. Available online through http://www.americanheart.org. Accessed February 2014.

Mandava P. et al. (Updated 2013 June 20). Homocystinuria/Homocysteinemia. Medscape Available online at http://emedicine.medscape.com/article/1952251-overview#a30 through through http://emedicine.medscape.com. Accessed February 2014.

Baloghova, J. et. al. (Upated 2013 July 24). Dermetologic Manifestations of Homocystinuria. Medscape. Available online at http://emedicine.medscape.com/article/1115062-overview through http://emedicine.medscape.com. Accessed February 2014.

(Updated January 6, 2013) National Newborn Screening and Genetics Resource Center. National Newborn Screening Status Report. Available online at http://genes-r-us.uthscsa.edu/sites/genes-r-us/files/nbsdisorders.pdf through http://genes-r-us.uthscsa.edu. Accessed February 2014.

(Updated May 26, 2013) The Screening, Technology And Research in Genetics (STAR-G) Project, Homocystinuria Factsheet. Available online at http://www.newbornscreening.info/Parents/aminoaciddisorders/CBS.html through http://www.newbornscreening.info. Accessed February 2014.

Sources Used in Previous Review

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 488-490.

Stewart. D. (2004 July 26, Updated). Homocystinuria. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001199.htm.

Picker, J. and Levy, H. (2005 August 15, Updated). Homocystinuria Caused by Cystathionine Beta-Synthase Deficiency. GeneReviews [On-line information]. Available online at http://www.genetests.org/query?dz=homocystinuria through http://www.genetests.org.

(2005 September 23) Homocystinuria. Genetics Home Reference, Homocystinuria [On-line information]. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria through http://ghr.nlm.nih.gov.

Genetic Fact Sheets for Parents, Amino Acid Disorders. Expanded Newborn Screening with Tandem Mass Spectrometry Financial, Ethical, Legal, and Social Issues [On-line information]. Available online at http://www.newbornscreening.info/Parents/aminoaciddisorders/CBS.html through http://www.newbornscreening.info.

(2005 May 02, Reviewed). Genetic Fact Sheets for Professionals, Amino Acid Disorders. Expanded Newborn Screening with Tandem Mass Spectrometry Financial, Ethical, Legal, and Social Issues [On-line information]. Available online at http://www.newbornscreening.info/Pro/aminoaciddisorders/CBS.html through http://www.newbornscreening.info.

Homocysteine May Trigger Strokes. JS Online. Available online at http://www.jsonline.com/alive/ap/feb01/ap-stroke-amino-ac021601.asp through http://www.jsonline.com.

Homocysteine: An emerging age-related cardiovascular risk factor. Geriatrics. April 1999.

Donald W. Jacobsen, PhD, FAHA. Director, Laboratory for Homocysteine Research, Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH. (Fellow, American Heart Association; American Association for Clinical Chemistry member).

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 541-543.

Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 434-435.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 574-577.

What Is Homocysteine? American Heart Association [On-line information]. Available online at http://www.americanheart.org/presenter.jhtml?identifier=535 through http://www.americanheart.org. Accessed May 2009.

(Updated 2008 July). Familydoctor.org. [On-line information] Available online at http://familydoctor.org/online/famdocen/home/articles/249.html through http://familydoctor.org. Accessed May 2009.

(2008 January). Homocystinuria. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria through http://ghr.nlm.nih.gov. Accessed May 2009.

(© 2009). Homocysteine, Folic Acid and Cardiovascular Disease. American Heart Association [On-line information]. Available online at http://www.americanheart.org/presenter.jhtml?identifier=4677 through http://www.americanheart.org. Accessed May 2009.

Baloghova, J. et. al. (2006 December 6). Homocystinuria. emedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1115062-overview through http://emedicine.medscap.com. Accessed May 2009.

(Updated 2008 December). Cardiovascular Disease (Non-traditional Risk Markers) - Risk Markers - CVD (Non-traditional). ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CardiacDz/CVDRiskMarkerNontrad.html through http://www.arupconsult.com. Accessed May 2009.

National Academy of Clinical Biochemistry. Laboratory Medicine Practice Guidelines: Emerging Biomarkers for Primary Prevention of Cardiovascular Disease and Stroke (2009) Homocysteine and Cardiovascular Disease Risk. Pg. 51. PDF available for download at http://www.aacc.org/members/nacb/LMPG/OnlineGuide/PublishedGuidelines/risk/Documents/PublishedGuidelines.pdf through http://www.aacc.org.

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